1. Field of the Invention
This invention relates to a color image forming apparatus such as a color copier or a color printer having a neural network with, for example, a back propagation learning algorithm which, when image forming conditions such as those optimum for a given light-sensitive material are not properly computed on the basis of the original image formation read from the document, provides appropriate image forming conditions to thereby learn the appropriate values of image forming conditions which are associated with said original image formation. Examples of computations that are assisted by such learning capability are the one for distinguishing between documents to be copied such as color photographic documents and color printed documents, and the computation of the exposing conditions in accordance with the specific type of document such as a color negative film, a color reversal film or one carrying an electrically processed image.
2. Description of the Prior Art
Color image forming apparatus including various color copiers and color printers are gaining increasing popularity these days. In order to produce satisfactory color image with these color image forming apparatus, good balance must be attained not only in colors but also in densities.
With most of these color image forming apparatus, in particular, color copiers, photographs and printed matter are used a color originals. However, different colorants are used in photographs and printed matter. Further, they have different spectral luminous efficiencies and require the use of copying materials having different spectral sensitivities. On account of these differences, the images of copies from photographic originals have had a different color balance than those from printed originals if they are duplicated under the same copying conditions. For example, color printed originals have a great overlap between the spectral density distributions of magenta and cyan inks. Thus, color printed originals have a high magenta density and color copiers that are adjusted to produce good copies of color printed originals are to be operated under copying conditions that provide suppressed magenta density. Therefore, if color photographic originals are duplicated under such image forming conditions, the production of magenta color is so limited as to form color copied images of green shades.
To deal with this problem, many methods and means have been proposed for distinguishing between various types of documents. However, the conventional approaches proposed so far require not only complicated techniques of identification but also many discriminant formulas, so they have no been completely satisfactory in terms of the accuracy of identification and the convenience of identifying techniques.
Under these circumstances, the assignee proposed in Japanese Patent Application Kokai Nos. Sho-63-128556, Sho-63-187139 and Sho-63-187140 a method for identifying a specific type of color document by a plurality of discriminant formulas using part or all of the values of measurement with a total of six sensors for the three primary colors, two sensors being assigned to each primary color and having sensitivity peaks at different wavelengths within the wavelength region of the light of one primary color. The assignee further proposed in U.S. Pat. application Ser. No. 07/413,557 an image forming apparatus that is capable of distinguishing color photographic originals at least from color printed originals or black-and-white originals from color documents by a single discriminant function using the values of measurement from the six sensors described above.
Speaking of printers of the type in which color pictures are obtained by printing a positive image on light-sensitive materials of a given size from transmission-type originals such as negative films and reversal films, the individual negative films or reversal films used as original documents are not equal in such conditions as exposing and processing conditions and will suffer from imbalance in colors and densities. Thus, it has been necessary to determine the exposing conditions that are associated with the original image information read from a specific document of interest with a color scanner so that optimum color reproduction can be achieved on the print irrespective of the state of that document (whether it is a negative film or reversal film).
The assignee already proposed methods for determining such appropriate exposing conditions to control the amounts of photographic printing and exposure. Japanese Patent Application Kokai Nos. Sho-52-23936 and Sho-54-28131 describe a method which comprises the steps of measuring the transmission density of a negative film on the basis of a plurality of specified image areas of said negative film, classifying the type of that negative film on the basis of the measured characteristic amounts of image, computing the amount of correction for exposure, and performing photographic printing in the amount of exposure corrected by addition of said computed amount. The assignee also proposed a system named ACCS (advanced computerized color scanner).
The methods the assignee proposed in Japanese Application Kokai Nos. Sho-63-128556, Sho-63-187139 and Sho-63-187140 have the advantage that they insure a higher precision in identifying the type of a specific original document than the prior art while adopting a simple identifying technique and providing ease of control. However, these methods suffer from the disadvantage of requiring a plurality of discriminant formulas.
To solve this problem, the assignee proposed an improved image forming apparatus in U.S. Pat. application Ser. No. 07/413,557. Using a single discriminant function, the improved apparatus automatically distinguishes color photographic originals at least from color printed originals or black-and-white originals and selects the proper image forming conditions (e.g. the amount by which color filters are adjusted and the amount of exposure) and the right kind of light-sensitive material according to the type of the identified color original, to thereby obtain an appropriately reproduced visible image. The precision of identification that can be achieved by this apparatus is very high but not as 100%, so once the discriminant function is set, setting another function is not easy to accomplish because of the need to collect much data and to process it over a prolonged time. To solve this problem, a further improvement in the accuracy of identification and ease of handling have been desired.
According to the methods descried by the assignee in Japanese Patent Application Kokai Nos. Sho-52-23936 and Sho-54-28131, as well as in the ACCS system proposed by the same assignee, various characteristic amounts associated with a plurality of specified image areas ar computed on the basis of photometric data for the light of three primary colors for several hundred pixels that are read from a transmission-type original such as a negative film or a reversal film, and the exposing conditions such as the amount of exposure or the amount of correction for exposure that are necessary for achieving optimum color reproduction on a print can be automatically determined irrespective of the state of the original by a corrective computing procedure using a predetermined statistical technique such as multiple regression analysis. However, the state of transmission-type originals is generally subject to substantial variations and in order to insure that fully appropriate exposing conditions are set according to an individual document to be duplicated, not only a huge amount of data must be stored but also complicated procedures are required to compute the necessary amount of correction using such huge data.
Even if general exposing conditions that are optimum for desired color reproduction are set irrespective of the variations in documents, optimum values for the color balance and density of a visible reproduced image will differ from person to person or are subject to the preference of individuals laboratories. Further, said optimum values will vary depending on the basic tone of a specific object or scene (e.g. a snow scene in a snowy country is rich in white shades whereas a sea in a tropical region is rich in blue shades), so the setting of standard exposure conditions is insufficient and need be modified in different ways depending upon such factors as the site of use. In fact, however, it is extremely cumbersome and difficult to modify the once set value according to each of these requirements.